1. Field of the Invention
The present invention relates to a color recording method for recording a color image by superposing a plurality of inks, and an apparatus using the same.
2. Description of the Prior Art
In the field of color recording and photographics, known techniques of recording color images with good fidelity include color modification methods using (1) masking equations and (2) Neugebauer equations. With recent developments in color recording techniques, conventional halftone image recording is changing from utilizing analog recording methods to utilizing digital recording methods.
Typical methods of analog halftone recording include color photographic and color electrophotographic methods. According to such methods, as shown in FIG. 1, three primary colors according to the subtractive color process, i.e., inks of yellow Y, cyan C and magenta M form a complete layered structure on a recording medium P.
Typical methods of digital halftone recording include multicolor superposition printing methods, ink jet recording methods, and binary recording by electrophotographic methods. According to these methods, as shown in FIG. 2(A), layers of inks of a plurality of colors do not form a complete layered structure.
Masking equations relating to the density of the recorded images are established based on the arithmetic mean method. These equations can be used for the superposition method shown in FIG. 1 in which the inks form a complete layered structure. However, the arithmetic mean method cannot be applied to the color superposition method shown in FIG. 2(A) wherein the inks form only a partial layered structure. Accordingly, satisfactory color modification or correction cannot be performed in accordance with the masking equations.
The Neugebauer equations are provided assuming a case wherein the superposition areas of the printing inks are indeterminate and the area factor of the superposition part is proportional to the product of the respective ink areas. Therefore, the Neugebaur equations can only be used if superposition of the printing inks is produced at random by screen corner processing or the like, as is the case in color superposition in printing. However, in the case shown in FIG. 2(A), satisfactory color modification cannot be performed either in accordance with the Neugebauer equations or the masking equations. In addition to this, the Neugebauer equations do not provide a general solution but only provide an approximate solution.
As may be seen from the foregoing, satisfactory color modification cannot be performed with the conventional masking equations or Neugebauer equations.
In order to perform satisfactory halftone recording or the like, black processing is sometimes performed wherein black obtained by superposing all the colors Y, M and C is recorded with black ink. In order to perform this processing, additional processing such as minimum value detection of the black data or under-color removal of the black component from the other color data is required. For this purpose, a memory for storing data, an arithmetic operation circuit for performing complex calculations, and so on are required. This results in slow operation speed.
Meanwhile, color copying machines have been devised which photoelectrically read a color original, perform color separation and produce a color image in accordance with readout signals. In a color copying machine of this type, optical energy of light reflected from or transmitted through the original significantly fluctuates depending upon the material of the original and the reading method. Furthermore, the color signals obtained by photoelectrically reading an original are relative to each other and not absolute values. Therefore, optical energy of an image reproduced in accordance with these signals may differ from that of the original, resulting in a poor image.